The present invention relates to methods and apparatus for forming metal layers on an integrated circuit (semiconductor) device, and more particularly, to forming a layer including tantalum.
Various integrated circuit (semiconductor) devices, such as memory devices, are designed to operate at high speeds and/or have large storage capacity. To provide increased speed or capacity in such devices, various semiconductor technologies have been developed directed to improving the integration density, reliability and/or speed of the semiconductor devices.
There are typically strict requirements for metal layers that are used for metal lines on such a semiconductor device. Furthermore, to increase the density of devices formed on a semiconductor substrate, the metal layer is generally formed as a multi-layer structure. The metal layer is generally formed by depositing aluminum or tungsten. However, the specific resistance of aluminum is typically about 2.8×10−8 Ωm (ohm-meters) and the specific resistance of tungsten is about 5.5×10−8 Ωm, so they are typically not desirable as a multi-layer structure. Accordingly, copper, which has relatively low specific resistance and good electro-migration characteristics, may be used as a metal layer.
Copper generally has a high mobility in silicon and silicon dioxide (SiO2). In addition, when copper is reacted with silicon and silicon dioxide, the copper may be easily oxidized. Therefore, it is known to suppress the oxidization of copper using a barrier metal layer. A titanium nitride layer is widely used as the barrier metal layer. However, the titanium nitride layer is generally not suitable as a barrier metal layer for copper because the titanium nitride layer may be required to have a thickness above 30 nm to restrain the mobility of the copper. Because the titanium nitride layer has a resistance proportional to the thickness thereof and high reactivity, the resistance is generally significantly increased when the titanium nitride layer has a thickness above 30 nm.
Therefore, it is known to use a tantalum nitride layer for the barrier metal layer. A tantalum nitride layer may restrain the mobility of the copper even when the tantalum nitride layer is thin and has low resistance. The tantalum nitride layer may also be suitable for metal plugs and metal wires for good step coverage and gap-fill degree thereof. Examples of tantalum nitride layers that can be used as barrier metal layers are disclosed in U.S. Pat. No. 6,204,204 (issued to Paranjpe et. al.), U.S. Pat. No. 6,153,519 (issued to Jain et. al.), and U.S. Pat. No. 5,668,054 (issued to Sun et. al.).
As described in U.S. Pat. No. 5,668,054, the tantalum nitride layer is deposited through a chemical vapor deposition (CVD) process using terbutylimido-tris-diethylamido-tantalum ((NEt2)3Ta═Nbut (hereinafter referred to as “TBTDET”) as a reactant. The process is carried out at a temperature above 600° C. as the specific resistance of the tantalum nitride layer may exceed 10,000 μΩcm when the process is carried out at a temperature of about 500° C. In addition, as the process is carried out at a relatively high temperature, the semiconductor device can be thermally damaged. It is also generally difficult to achieve a tantalum nitride layer having superior step coverage using a CVD process.
An atomic layer deposition (ALD) process has been suggested as an alternative to the chemical vapor deposition process. The atomic layer deposition process can be carried out at a relatively low temperature as compared with a conventional thin film forming process and can achieve superior step coverage. Examples of ALD processes for depositing tantalum nitride are disclosed in U.S. Pat. No. 6,203,613 (issued to Gates) and in an article by Kang et al., entitled “Plasma-Enhanced Atomic Layer Deposition of Tantalum Nitrides Using Hydrogen Radicals as a Reducing Agent,” Electrochemical and Solid-State Letters, 4(4) C17–19 (2001). As described in the Kang et al. article, a tantalum nitride layer having a specific resistance about 400 μΩcm can be formed by the ALD process using TBTDET. The deposition is carried out at a temperature of about 260° C. Accordingly, a tantalum nitride layer having a low specific resistance may be formed at a relatively low temperature.
However, a hydrogen radical obtained by a plasma-enhanced process is used as a reducing agent in the Kang et al. process. Accordingly, a power source is applied to the chamber during deposition. For this reason, the process described by Kang et al. has process parameters that may be influenced by the power source applied to the chamber. Thus, while the Kang et al. process describes forming a thin film at a relatively low temperature, the process includes controlling additional process parameters, such as the power source. Moreover, because the Kang et al. process includes applying the power source directly to a predetermined portion of the chamber in which a semiconductor substrate is placed, the semiconductor substrate can be damaged by the power source.